2002 Ford Taurus When heating system is turned on noise and

When i turn on the heating system (in either defroster or blower at driver settings) i hear a click on, a very quick tick..(like 10 per second) then it cuts out again, and repeats. Noticed first when driving, it robs power when it clicks on then off...making for a sluggish feeling in the car..as if someone was turning on and off the AC in the summer. I have an 02 taurus SES 24 valve DOHC. I've heard that the AC comes on and off with the heating system..however, why does it turn on, and off and on and off (about every 2 seconds or so) when i turn it on. It blows hot air...but it's still obviously a concern. I'm curious if it's an AC problem, or a relay issue, or something of that nature. Thank you for your time.